For barricade shooting they want the weight in front of the mag well, for bench shooting we want the weight back a bit further to the rear of the magazine or near the trigger. Getting the weight moved to the rear will let the rifle settle into and ride on the rear bag better. We need to keep the center of gravity at least 1/2 ways between the rear rest and the front rest. This will help with any muzzle moments but help mangae the recoil better as well.
As an experiment I took at cheap savage FV12 223 and filled the butt stock with bondo and Lead shot. The 8lb rifle turned into the 19lb rifle. The balance is near the back of the triggers or just into the grip. I have found this quite comfortable. I did notice it takes different fundamentals to shoot. It shoots much better groups in a bench rest style where I don't touch it much or manage the recoil (mostly because I don't have to).
I'd try it with the weights first, you can always take them off later (or add them later as well)
